This invention relates to peroxide-curable fluoroelastomer compositions having improved compression set resistance. More specifically, the present invention is directed to certain peroxide-curable bromine-containing fluoroelastomer compositions that contain trimethallylisocyanurate thereby significantly improving the compression set resistance of vulcanizates of such compositions when such compositions have been compressed, subjected to high temperatures, and subsequently cooled and held under compression at about room temperature.
Peroxide-curable bromine-containing fluoroelastomers have been favorably accepted by the industry. Such fluoroelastomers are described in U.S. Pat. No. 4,214,060. These fluoroelastomers when cured have good resistance to damage by heat, solvents and corrosive chemicals, are especially resistant to degradation by steam, and have good compression set resistance at high temperatures of the order of about 150.degree.-200.degree.C. The peroxide-curable bromine-containing fluoroelastomer compositions of the present invention are frequently used under conditions in which temperature variations are extreme. When such fluoroelastomer compositions are fabricated into, for example, seals, due to the degree of crystallinity of these fluoroelastomers when the seals are subjected to alternating heating and cooling cycles, the fluoroelastomers develop poor compression set resistance at lower temperatures, e.g., room temperature, after the fluoroelastomer has been subjected to high temperatures. The result is that due to the poor compression set resistance of the fluoroelastomers at lower temperatures the seals will leak. Thus, the compression set resistance of peroxide-curable bromine-containing tetrapolymers leaves much to be desired when the vulcanizates of such compositions are heated to relatively high temperatures of the order of 200.degree. C. and subsequently cooled while under compression and held under compression at about room temperature, which are conditions that frequently occur in use. The present invention provides a novel bromine-containing fluoroelastomer composition that retains the advantages of prior art peroxide-curable fluoroelastomers but, in addition, the fluoroelastomer compositions have improved compression set resistance at about room temperature i.e., 20.degree.-25 .degree.C., even after the fluoroelastomer compositions are heated to elevated temperatures of the order of about 200 .degree.C. and then cooled to about room temperature while under compression.